Luteinizing Hormone and Testosterone Concentrations in Plasma of Bull Calves Treated with Gonadotropin Releasing Hormone

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Abstract
Twelve bull calves, 2-24 days of age, were assigned to 2 groups of 6 calves and administered a single 50 .mu.g i.m. injection of gonadotropin releasing hormone. Bull calves in group 1 were 2-5 days of age (mean 3.0 days), and bull calves in group 2 were 10-24 days of age (mean 17.1 days). Blood plasma for radioimmunoassay of luteinizing hormone [LH] and testosterone [T] was collected at .5 h intervals for 3 h and at 4- and 6-h following treatment. With increasing age, preinjection LH concentrations in plasma decreased while preinjection T concentrations increased. Mean preinjection LH concentrations for group 1 (1.01 .+-. .07 ng/ml; mean .+-. SE) were higher than for group 2 (.61 .+-. .+-. .12 ng/ml). Preinjection LH and T concentrations were correlated -.63. Following treatment, LH increased with mean peak concentrations of 7.28 .+-. .74 and 6.95 .+-. 1.79 ng/ml for groups 1 and 2. Peak T response following gonadotropin releasing hormone was higher for group 2 than 1 (1077 .+-. 253 vs. 436 .+-. 116 pg/ml).